Infrared emitting gas burner

ABSTRACT

A gas burner for an infrared oven provides fast and controllable infrared energy, the emitted spectrum of which varies continuously over a wide spectrum. The burner is assembled from an elongated fuel distribution chamber having an open top and into which a gaseous fuel and combustion air is introduced. As the fuel mixture is delivered into the fuel distribution chamber, it eventually fills the chamber and thereafter flow through a double-layer wire mesh burner plate set over the fuel distribution chamber. The fuel combusts above the wire mesh burner plates to heat a screen wire above the burner plates. The screen wire is heated to a temperature at which the screen wire emits IR. The emitted IR wavelength can be controlled by controlling the gas supply to turn the combustion on and off according to the amount of IR heated needed.

BACKGROUND

Infrared (IR) energy is known to be able to cook certain types of foodsfaster than convection energy. Although IR is not as fast as microwaveenergy, IR energy is known to produce better cooking results thanmicrowaves.

A problem with cooking using IR is that generating short-wavelength IR,which penetrates food deeper than long wavelength energy, typicallyrequires a relatively large amount of energy because high temperaturesare needed to adequately heat a surface to emit short-wavelength IR.Because short-wavelength IR almost always requires a very hightemperature surface, generating short-wavelength IR therefore oftenrequires additional time to generate. Another problem with IR cooking isthat it is more difficult to control than convection heating.

An oven that is able to quickly, efficiently and controllably generateinfrared energy for cooking different types of foods would be animprovement over the prior art.

SUMMARY

A gas burner for an IR oven can quickly, efficiently and controllablygenerate short-wavelength IR as well as long-wavelength IR by combustinga gaseous fuel just below a low mass, low-specific heat burner screenuntil it emits IR. The gas supply is preferably cycled on and off, inorder to allow the burner screen to absorb heat energy from combustingfuel until it reaches a desired temperature. The gas supply is then shutoff to allow the burner screen to dissipate IR and cool, which testingshows will extend the burner screen's useful lifespan.

DRAWING DESCRIPTION

FIG. 1 is an exploded perspective view of a gas burner;

FIG. 2 shows a top view of the burner shown in FIG. 1;

FIG. 3 shows a cross sectional view through the burner of FIG. 1 andFIG. 2 through section lines III-III; and

FIG. 4 shows an isolated view of the connection of wire mesh burnerplates used in the burner.

DETAILED DESCRIPTION

FIG. 1 shows a perspective view of a gas burner 10 for an oven, notshown. The burner 10 is comprised of a fuel distribution chamber 12. Inone embodiment, the distribution chamber is in the shape of a cuboid orrectangular parallelepiped having a bottom 14, four sides 16A-16D, buthaving an open top 18 through which a gas/fuel mixture flows asdescribed below. The fuel distribution chamber 12 has a length, L, widthW, and a depth D.

A fuel inlet pipe 20, with first and second opposing and open ends 22and 24, extends through one of the sides 16A of the distribution chamber12. As can be seen in FIG. 3, the fuel inlet pipe 30 length, is morethan half the length, L, of the distribution chamber 12 such that itssecond end 24 is between about 4 and 10 inches from a gas flow diverter28. A gaseous fuel, such as natural gas or liquid propane, is introducedinto the open end 22, which is outside the distribution chamber 12.Combustion air is also introduced into the open end 22 of the fuel inletpipe 20 from a blower, not shown, which supplies combustion air andwhich forces the fuel gas and combustion air mixture through the fuelinlet pipe 20, causing the mixed gases to strike the diverter 28 andmove back toward the first side 16A of the chamber 12.

In FIG. 3, it can be seen that the fuel inlet pipe 20 is constructed bytelescoping a short section of pipe S1 inside a larger-diameter andlonger second pipe S2. Close inspection of FIG. 3 reveals that the firstsection of pipe S1 fits just inside the second and longer second sectionof pipe S2. Since the outside diameter of the first section of pipe S1is less than the inside diameter of the second section S2, the insidediameter of section S1 is also less than the inside diameter of thelonger section of pipe S2.

At a point 21 located approximately half-way between the first end 22and second end 24 of the fuel inlet pipe 20, a discontinuity in theS1/S2 pipe diameters is formed by the termination of the pipe section S1within S2. In other words, at the point identified by reference numeral21, the inside diameter of the fuel distribution pipe 20 is stepped upor increased, causing a small but non-zero pressure drop at point 21.The discontinuity 21 is believed to create additional turbulence, whichaids in the mixing of fuel and combustion air together. At the second ordistal end 24 of the fuel inlet pipe 20, the fuel and combustion airleave the fuel inlet pipe 20, strikes the diverter 28 and from which itcan evenly fill the distribution chamber 12.

As can be seen in FIG. 3, the fuel inlet pipe 20 runs along almost theentire length of the distribution chamber 12. Fuel and air that leavesthe fuel inlet pipe 20 at its second end 24, strikes the diverter 28,which is sized, shaped and arranged to re-direct or divert gases leavingthe fuel inlet pipe 20, back toward the first side 16A of thedistribution chamber 12. The diverter 28 is semi-circular or U-shaped,having a radius of curvature that is just slightly less than theone-half the distribution chamber depth D.

It is important that an oven be heated evenly and uniformly so that theoven's interior space can be fully utilized, especially so in acommercial oven, such as those used to cook pizza. In order to provideeven and uniform heat, the fuel and air that leaves the second opening24 fills the fuel distribution chamber 12 and flows upwardly into one ormore wire mesh burner plates 32, that are placed over the open top 18 ofthe distribution chamber 12.

As shown in FIG. 1 and FIG. 3, the wire mesh burner plate assembly 30 iscomprised of several individual wire mesh burner plates 32 that areattached to each other so that they abut each other. The assembly 30 ofwire mesh burner plates 32 is laid over the open top 18 of the burner 10distribution chamber 12. The wire mesh burner plates 32 and thecomposite plate 30 formed of several individual burner plates 32, areboth described and claimed in the applicant's co-pending U.S. patentapplication having Ser. No. [ t.b.a.] and which is entitled WIRE MESHBURNER PLATE FOR A GAS OVEN BURNER. The entire disclosure of U.S. patentapplication Ser. No. [t.b.a.] is incorporated herein by reference. Ascan be seen in the co-pending application Ser. No. [t.b.a.] for the WireMesh Burner Plate for a Gas Oven Burner and as can be seen in FIG. 3,several individual wire mesh burner plates 32 are coupled together overthe open top of the burner distribution chamber 12. Fuel combustiontakes place above the wire mesh burner plates 32.

Fuel and combustion air from the distribution chamber 12 enters openspace within the wire mesh burner plates 32 where they mix together. Asthe fuel and air continue to flow into the burner plates 32, the fueland air eventually flows out of the “top” of the burner plates 32 whereit is ignited by a pilot flame (not shown), which is lit by an electricigniter controlled by a controller. The pilot light causes the fuel andair mixture leaving the top of the burner plates 32 to ignite andcombust. The continued supply of fuel gas and combustion air from thedistribution chamber 12 allows the combustion to continue, which in turnheats a wire mesh burner screen 36 spaced above the burner plates 32 andthe burner plate assembly 30. A gasket 34 that surrounds the burnerplates 32 (See FIG. 2.) prevents the fuel and combustion air mixturefrom leaking from the sides of the burner plates 32 and helps to insurethat all of the fuel is burned.

Infrared heat energy is quickly and controllably generated by thecombustion of fuel gas below the wire burner screen 36, which preferablyof a low mass and therefore quickly heated. The combustion of the fuelbeats the wire burner screen 36 until it is hot enough to emit infrared.Once a desired IR emission is reached, the fuel gas is preferably shutoff by a computer (not shown), after which IR will continue to beemitted as the burner screen 36 temperature drops. When IR emissiondrops to some empirically determined value, the burner can be re-lit bythe controller (not shown) to re-heat the screen 36 and generate moreIR. Since the burner screen 36 will be cooler when the burner 10 isre-lit, heat transfer efficiency from the combusting fuel to the screen36 will be greater than when the burner screen 36 is continuouslyheated. By cycling the gas supply on and off, the energy transfer intothe screen 36 can be improved over what it would be if the gas supplywere simply left on during a cooking process. In addition, by cyclingthe wire screen 36 temperatures, the IR wavelength emitted from the wirescreen 36 cyclically varies from relatively short-wavelength anddeeply-penetrating visible IR emitted at high temperatures, torelatively long-wavelength, less-penetrating IR emitted at relativelylow temperatures. By cycling the gas supply, the screen 36 can be madeto emit IR across a continuously varying spectrum of wavelengths.

The fuel combustion that heats the burner screen 36 takes place abovethe burner plates 32 but below the burner plate screen 36, which is heldin a spaced-apart relation above the burner plates by spacers as shown,with the preferred space being about one-half inch. The spacing betweenthe burner plate screen 36 and the burner plate assembly 30 (or theindividual burner plates 32) define a combustion space 38, the height ofwhich is chosen to provide a space large enough to allow the fuel tofully combust below the burner plate screen 36 in order to maximize heattransfer into the burner plate screen 36.

As the height of the combustion space 38 decreases, some of thecombustion process will occur above the burner plate screen 36, reducingheat transfer into the screen 38. Conversely, as the combustion space 38increases, the combustion process will finish below the burner platescreen 38, allowing the combustion products to cool and external air tobe drawn into the combustion space 38, thereby reducing heat transferinto the screen 38. Thus, there is an optimal spacing of the heattransfer screen 36 above the burner plates 32 that will maximize heattransfer for a given flow rate of fuel and combustion air into theburner 10. In a preferred embodiment, the burner plate screen 36 isabout one-half inch above the burner plates 32, however, spacing assmall as about one-quarter inch up to about one inch can also be used.

In one embodiment, the burner plate screen 36 is nichrome wire, however,alternate embodiments include using steel and stainless steel wire, withand without heat-tolerant coatings such as ceramic. In yet anotherembodiment, the burner plate screen 36 is made entirely of ceramic.

By combusting gas below a low-mass, low-specific heat screen, the screen36 can be quickly heated to temperatures where the screen will emitshort-wavelength and deep-penetrating infrared energy. By cycling thefuel supply on and off, the screen 36 is allowed to cool during gas-offtime periods, during which time it will emit increasingly longerwavelength IR. Testing shows that rapid heating and cooling cycles alsoextends the screen's 36 life beyond the life it would have if the screen36 were heated continuously.

The foregoing description is for illustration and not for limitation.The scope of the invention is defined by the following claims.

1. A gas burner for an oven comprising: an elongated fuel distributionchamber (distribution chamber) having an open top; a fuel inlet pipethat extends through the distribution chamber by a first distance, saidfuel inlet pipe having a first open end outside the distribution chamberinto which gas fuel is introduced, said fuel inlet pipe having a secondopen end opposite the first open end from which fuel enters thedistribution chamber; at least one wire mesh burner plate, which extendsover the open top of the distribution chamber; a burner plate screen,spaced above and extending over at least part of the at least one wiremesh burner plate; wherein a fuel/air mixture combusts substantiallyabove the at least one wire mesh burner plate in order to heat theburner plate screen to emit infrared heat.
 2. The gas burner of claim 1,further comprising a gas flow deflector within the distribution chamberssaid fuel being directed toward the gas flow deflector, the gas flowdirector redirecting at least some of the fuel and air within thedistribution chamber.
 3. The gas burner for an oven of claim 1, whereinthe burner plate screen is spaced above the at least one wire meshburner plate by a first distance that defines a space wherein thefuel/air mixture combusts.
 4. The gas burner of claim 1, furthercomprised of a gasket around the at least one wire mesh burner plate. 5.The gas burner of claim 3, wherein the first distance is between aboutthree-fifths of an inch and about one inch.
 6. The gas burner of claim3, wherein the first distance is approximately one-half inch.
 7. The gasburner of claim 1, wherein the burner plate screen is comprised of anichrome wire.
 8. The gas burner of claim 1, wherein the burner platescreen is comprises of a ceramic-coated metal.
 9. The gas burner ofclaim 1, wherein the burner plate screen is comprised of ceramic. 10.The gas burner of claim 1, wherein the combustion chamber is comprisedof stainless steel.
 11. A gas burner for an oven comprising: anelongated fuel distribution chamber (distribution chamber) having abottom, four sides and an open top, the fuel distribution chamber havinga length, width and depth; a fuel inlet pipe having that extends througha first side of the distribution chamber and through the distributionchamber by a first distance that is less than the distribution chamberlength, said fuel inlet pipe having a first open end located outside thedistribution chamber and into which gas fuel and combustion air isintroduced, said fuel inlet pipe having a second open end opposite thefirst open end and from which fuel and combustion air enters thedistribution chamber, said fuel inlet pipe also having an insidediameter and a discontinuity in said inside diameter; at least one wiremesh burner plate, which extends over the open top of the distributionchamber; a burner plate screen, spaced above and extending over the atleast one wire mesh burner plate; wherein a fuel/air mixture combustsabove the at least one wire mesh burner plate after the fuel/air mixturepasses through the at least one wire mesh burner plate and thedistribution chamber.
 12. The gas burner of claim 11, further comprisinga gas flow deflector spaced away from the second open end of the fuelinlet pipe and located within the distribution chamber, said gas flowdirector directing at least some of the fuel exiting the second open endof the fuel distribution pipe to travel through the distribution chambertoward the first end of the distribution chamber.
 13. The gas burner foran oven of claim 11, wherein the burner plate screen is spaced above theat least one wire mesh burner plate by a first distance, the firstdistance defining a space between the at least one wire mesh burnerplate and the burner plate screen wherein the fuel/air mixture combusts.14. The gas burner of claim 11, further comprised of a gasket around theat least one wire mesh burner plate.
 15. The gas burner of claim 13,wherein the first distance is between about three-fifths of an inch andabout one inch.
 16. The gas burner of claim 13, wherein the firstdistance is approximately one-half inch.
 17. The gas burner of claim 11,wherein the burner plate screen is comprised of a nichrome wire.
 18. Thegas burner of claim 11, wherein the burner plate screen is comprises ofa ceramic-coated metal.
 19. The gas burner of claim 11, wherein theburner plate screen is comprised of ceramic.
 20. The gas burner of claim11, wherein the combustion chamber is comprised of stainless steel.